There is a need for a driving assist system, which can reliably assist effort by an operator to operate a vehicle, such as, an automobile, in traveling. Currently available automobiles are equipped with a data acquisition system and a controller including a processor. Such data acquisition system can continuously acquire data including information on vehicle state, such as current vehicle velocity, and information on environment in a field around the vehicle. The information on environment includes the presence of obstacles, including a leading vehicle ahead. Ideally, a driving assist system should avoid objection by the operator of the automobile in assisting the operator manual effort to reduce a risk of collision with an obstacle. However, if the vehicle should encounter risky environment involving the presence of an obstacle, the driving assist system should avoid collision with the obstacle. Thus, there is a need for a system, which performs assist so that the operator can continue driving comfortably without any objectionable feel due to such assist.
JP-A 10-211886, published on August 11, discloses a steering control system, which modulates power-assist for avoidance of collision upon recognition of a risk within a field around the vehicle. This steering control system computes the magnitude of risk with respect to each of obstacles within the field around the vehicle. The magnitude of risk reflects the magnitude of impact upon collision with the obstacle. The magnitude of impact depends mainly upon the relative velocity between the vehicle and the obstacle. Accounting for this fact, the known system computes an individual risk R(i) from an angular location α(i) expressed in terms of an azimuth angle of an obstacle i, a distance or separation d(i) between the subject vehicle and the obstacle i, and an odd function of the relative velocity Vref(i) between the subject vehicle and the obstacle i. This odd function involves a term of Vref(i)n (n=a real number grater than or equal to 3). The individual risk R(i) is expressed as,
                              R          ⁡                      (            i            )                          =                                                            f                ⁡                                  (                                      Vref                    ⁡                                          (                      i                      )                                                        )                                            +              k                                      d              ⁡                              (                i                )                                              ⁢                      W            ⁡                          (                              α                ⁡                                  (                  i                  )                                            )                                                          Eq        .                                  ⁢        1            where,    f(Vref(i))=Odd function that involves a term of Vref(i)n (n≧3);    d(i)=Distance (or separation) between the subject vehicle and the obstacle i;    k=Constant to adjust the distance d(i); and    W(α(i))=Weighting component applied to the obstacle i appearing in the angular location α.The individual risks are summed vertorially to produce a resultant risk R, which is expressed as,
                    R        =                              ∑            i                    ⁢                      R            ⁡                          (              i              )                                                          Eq        .                                  ⁢        2            
The known steering control system is capable of avoiding collision with the obstacle by assisting the operator to operate the vehicle laterally to clear the obstacle. However, this system appears to be insufficient to avoid objectionable feel, which the operator might have. The operator may have such objectionable feel upon occurrence of a power assist, which has magnitude determined by the risk R, because a discrepancy exits between the risk R and a risk that is perceived by the operator. When the vehicle encounters an obstacle, the magnitude of risk R is proportional to the cube of the relative velocity between the vehicle and the obstacle, whereas the magnitude of risk perceived by the operator is proportional to the square of the relative velocity.
It is therefore an object of the present invention to provide a driving assist system for assisting effort by an operator to operate a vehicle in traveling, which can assist the operator without causing the operator to have any objectionable feel.
It is another object of the present invention to provide a simple and economical driving assist system for assisting effort by an operator to operate a vehicle in traveling.